For such overlay alloys and the sliding materials there have been conventionally used such alloys as Pb-Sn alloy, Pb-In alloy, Pb-Sn-Cu alloy and Pb-Sn-In alloy and sliding materials having those alloys as surface layer, those alloys and sliding materials being, for example, shown in "Materials for sliding bearing" by Kazuyuki Morita, Engineer, September 1967, page 44; "Recent trend of materials used for sliding bearing" by the same author, Engineer, April '70, pp 90; Japanese Examined Patent Publication No. 42128/1977; and U.S. Pat. No. 2,605,149. Japanese Examined Patent Publication No. 9635/1982 discloses a technique for making overlay alloy wherein an electroplating method having two steps of plating and a step of heat diffusion are utilized.
Because of recent remarkable progress concerning automotive internal combustion engines and other industrial machinery in which higher speed and higher load become possible, conventional sliding materials for sliding parts and the like used for such machinery have caused, when constituted by the above- mentioned conventional overlay alloys, several problems including a shorter service life of bearing experienced particularly under operational conditions of high speed and high load due to insufficient lubricant film which in turn deteriorates wear resisting property, fatigue resisting property and corrosion resistance, etc. Furthermore, since in a case of sliding bearing so-called cavitation erosion is inherent in which the erosion of the surface layer of a sliding bearing is caused in lubricant oil, it has also become necessary to prevent or minimize damages caused in the sliding bearing due to the cavitation erosion. Conventional overlay alloys such as Pb-Sn alloy, Pb-In alloy and Pb- Sn-In alloy have been not preferred due to large degree of cavitation erosion In view of this fact, it has been desired in this technical field to obtain a sliding material having a cavitation-erosion resisting property improved in the same degree as in conventional Pb-Sn-Cu overlay alloy.
JA No. 84435/1981 (corresponding to U.K. published application No. 2,060,692A) discloses a bearing of an internal combustion engine having an overlay layer of a generically disclosed alloy with very broad ranges of Sn, In, Cu and Pb. The most interesting of the examples are those of samples 2, 9, 18 and 19; however, samples 2, 18 and 19 have a percentage of copper which is too low to provide adequate seizure property. Sample 9 has a percentage of copper of 3%, but contains 17% of tin, an amount which causes the tin to diffuse into an underlayer which, if made of copper alloy, causes a Cu-Sn reaction layer which is thick and brittle.
A later Japanese published application No. 205442 of November 1984 indicates that the alloys of the aforementioned JA No. '435 are not satisfactory because the quaternary alloys thereof are insufficient in compatibility and wear resistance for contemporary high speed engines. Instead, quaternary alloys are suggested having a minimum of more than 10% of In. However, these alloys are not satisfactory because an In content more than 10% causes a poor load capacity.
The Vandervell Australian Pat. No. 135,046 and the equivalent Canadian Pat. No. 515,808 disclose a bearing layer composed of lead with which from 1-10% of In, 0.1-5% Sn and 0-2% Cu have been alloyed. This is insufficient copper to provide improved seizure property.
Also of interest is the Vandervell Canadian Pat. No. 487,310 which sets forth a range in a quaternary lead alloy of 0.1-3% Cu, 0.5-15% In and 3-15% Sn. the only example constituting 10% Sn, 5% In, 1% Cu with the balance being lead. This alloy contains insufficient copper and too much tin.